Module terminals are frequent mission rewards from scan missions in Quince system.
In order to get the permit for the Sirius system, you need to go to Proclyon system AFTER getting Allied with Sirius Corp(Sothis , CEO's, Avik systems).
At Proclyon, you land at the main starport, and look at the mission board for a Mission that states Sirius system permit.
If it's not on the board when you check, run a few missions and come back and refresh the board. The permit mission is RNG and is random. It will only spawn at one station at a time and may not be the main starport at the time you arrive.
You cannot land at Palin's base without the actual invitation being offered first....the base simply won't appear on the surface of the planet for you until you have that invitation.